This invention relates to the field of metal surface finishing and in particular to the process of using ultrasonic cavitation to accomplish such finishing.
Within numerous manufacturing industries, metal components such as those composed of aluminum can require various finishing processes. In the semiconductor tooling industry, two of these finishing processes for aluminum tools include (1) xe2x80x9cjitterbuggingxe2x80x9d for applying a suitable cosmetic appearance to exposed aluminum surfaces, and (2) polishing for adequately smoothing a surface to provide it with sufficient sealing capability and to reduce its imperfections.
Jitterbugging a surface normally involves manually sanding the surface with vibratory sanding in conjunction with bonded abrasive grain media or fiber pads. This creates a desired dull xe2x80x9cmattexe2x80x9d finish. In the semiconductor tooling industry, this jitterbug finish has generally become somewhat of an industry standard for exposed aluminum surfaces.
Unfortunately, because the surfaces are processed manually, the required quality of jitterbug finishing is difficult to define, document, or repeat. In addition, excessive human resources are required for jitterbugging the surface of a conventional tool.
Moreover, while the jitterbugged surfaces appear to be cosmetically uniform due to their diffusive appearance, a typical surface without any additional polishing will include lengthy, continuous traces resulting from the use of abrasive materials. These lengthy traces (or scratches) tend to impair the surface""s sealing capability. Chemical cleaning can greatly improve the surface morphology, but it does not completely eliminate the traces. In addition, such chemical cleaning will not sufficiently reduce the surface""s porosity. Thus, polishing is applied to portions of surfaces that require sealing capability or have porosity threshold requirements.
Polishing metal surfaces in order to improve their sealing capability also involves significant manual effort and resources. In addition, traditional polishing processes are not always effective for attaining necessary sealing capabilities. Moreover, some surfaces have complicated or intricate geometries that are not even amenable to conventional polishing.
Accordingly, a need exists for an improved process for finishing metallic surfaces.
The present invention provides such an improved finishing process and apparatus. In one embodiment, a method and apparatus are provided for finishing a metal article. The method includes cavitationally eroding the metal article to form pits in its external surface. The metal article is also corroded with a corrosion chemical to corrode the pitted metallic surface. In this manner, substantially homogeneously distributed micro-pits can be formed about the article to create a desired matte finish, as well as a surface that is amenable for sealing. In a preferred embodiment, the corrosion chemical is part of a finishing bath that is ultrasonically cavitated for eroding the metal article.